The disclosure relates generally to power generation, and more particularly to optimization of power generation in a power plant that includes a thermal generator, such as a gas turbine.
In power generation, it is common to use thermal generators, such as gas turbines and combined cycle power plants, to generate electricity in a power system. Such a power plant typically includes a power plant control system that may generate an offer curve or a set of offer curves representing cost of power production by the power plant. For example, an offer curve may include an incremental variable cost curve, an average variable cost curve, or another suitable indication of power generation cost, typically measured and/or expressed in dollars per megawatt-hour versus power plant output in megawatts.
As is known, an average variable cost curve may represent a cumulative cost divided by a cumulative power output for a given point, and an incremental variable cost curve may represent a change in cost divided by a change in power output for a given point. An incremental variable cost curve may be obtained, for example, by taking a first derivative of an input-output curve of the power plant that may represent cost per hour C versus power generated Pg. In other words, if cost per hour is represented byC=RK,                R=fuel rate, K=fuel cost,then incremental cost IC may be represented by:        
  IC  =                    ⅆ        C                    ⅆ                  P          g                      =          K      ⁡              (                              ⅆ            R                                ⅆ                          P              g                                      )            In a combined cycle power plant in which waste heat from a fuel burning generator is used to produce steam to power a supplemental steam turbine, an incremental variable cost curve may also be obtained with known techniques, but its derivation may be more complex.
The power plant control system may send the offer curve(s) to a power system controller of an authority, such as an independent system operator in a deregulated market or a utility company in a regulated market, and may do so periodically. For example, some power plant control systems send an offer curve daily, and some even send the same, predefined offer curve every time, not taking unit degradation or changing ambient and/or market conditions into account.
The power system controller may receive offer curves from other power plants under its control and evaluate all offer curve(s) received to determine which power plants should be engaged and for how much power, such as by generating a unit commitment and/or dispatch schedule. Generation of a unit commitment and/or dispatch schedule typically includes consideration of a future time period or prediction horizon. While the future time period has typically been on the order of one or more days, more recent systems consider smaller time periods, such as an hour or fifteen minutes, so that power system control approaches real time control.
The power system controller generates the unit commitment and/or dispatch schedule and sends or communicates the control signals to the power plants. These control signals may include a target load for a respective power plant. Each power plant control system may then determine an appropriate set point for an operating parameter such that it can meet the target load, and each power plant control system may include its own optimization routines to optimize power plant operation. However, such optimization routines do not take life cycle cost of the power plant into account, particularly in generating an offer curve.
In general, gas turbine life, for example, may be measured in hours of operation and/or number of starts from an initial time of readiness for operation. If a gas turbine or a part of a gas turbine reaches its starts limit before its hours limit, it must be repaired or replaced, even if it has hours-based life remaining. Hours-based life in a gas turbine may be prolonged by reducing firing temperature, but this reduces efficiency of the gas turbine, increasing cost of operation. Conversely, increasing the firing temperature increases efficiency, but shortens gas turbine life and may increase maintenance and/or replacement costs. Thus, life cycle cost may be affected by changing the manner in which a power plant is operated.